Transmission and distribution planning procedure

Power system planning is the systematic process of deciding the future additions to generation, transmission and distribution facilities, with their type, size, location and time of installation, so that forecast load is supplied reliably, economically and with acceptable environmental impact.

It has four linked parts: load forecasting, generation expansion planning, transmission expansion planning and distribution planning.

Transmission expansion planning procedure

1. Inputs: Load forecast at each grid substation, generation expansion plan (where and when new plants come), existing network data, cross-border plans.
2. Planning criteria: N-1 security, voltage within ±5%, line loading within thermal limit, fault level within breaker rating, stability.
3. Base-case studies: Load flow for future years and seasons to identify overloads, low voltages and generation that cannot be evacuated.
4. Candidate alternatives: New lines, voltage upgrading (132 → 220/400 kV), double circuit, new substations, reactive compensation.
5. Technical analysis: Load flow, contingency, short-circuit and stability studies.
6. Economic analysis: Compare present worth of capital cost + loss cost + outage cost; choose least-cost plan.
7. Implementation plan: Routes, right-of-way, schedule and financing.

Distribution planning procedure

1. Spatial load forecast: Forecast load by area/feeder using land use, new settlements and consumer growth.
2. Study existing system: Feeder loading, voltage drop, losses, reliability indices (SAIFI, SAIDI).
3. Set criteria: Voltage drop limit (e.g. 5–10%), feeder loading, loss target, reliability target.
4. Substation planning: Location and size of 33/11 kV substations; distribution transformer siting.
5. Feeder planning: New feeders, reconductoring, feeder reconfiguration, ring mains in cities.
6. Loss reduction and reliability measures: Capacitors, voltage regulators, automation, smart meters, underground cabling.
7. Economic evaluation: Choose the least-cost combination meeting the criteria.
8. Implementation and review: Phased construction; update every few years.

 Load forecast
   |
 Generation planning --> Transmission planning
                               |
                      Distribution planning

Example: NEA's Kathmandu Valley distribution plan converts overhead lines to underground cables and adds new 132/11 kV substations to meet urban growth.